Electrical insulation oil

ABSTRACT

An electric insulating oil having excellent electrical insulation properties is obtained by incorporating in silicone oil at least one member selected from the group consisting of alkyl fluoranthenes of the generic formula   AND ALKYL PYRENES OF THE GENERIC FORMULA   WHEREIN, R denotes an alkyl group having from one to four carbon atoms and x denotes an integer having a value of from 1 to 4, and when x is an integer of 2 or more, R may be the same or different.

United States Patent [191 Ogura et al.

[ ELECTRICAL INSULATION OIL [75] Inventors: Jiro Ogura; Ikuo Seki; Kiyotaka Sato, all of Hitachi; Masaaki Takahashi; Akita Ito, both of Tokyo; Yuriko Igarashi, Mitaka, all of Japan [73] Assignee: Kureha Kagaku Kogyo Kabushiki Kaisha, Tokyo, Japan (22] Filed: Sept. 30, 1974 [2]] Appl. No.: 510,224

[30] Foreign Application Priority Data Oct. 4, I973 Japan a. 48-] l I869 Nov. l5, 1973 Japan 48-127669 [52] US. Cl. 252/63.7; l74/l10 S; 252/63; 252/78 [51] Int. CL .t H01B 3/18 [58] Field of Search 252/617 63, 78; l74/l l0 S [56] References Cited UNITED STATES PATENTS 2,340,644 2/1944 Clark 252/632 FOREIGN PATENTS OR APPLICATIONS 538,41 l 8/l94l United Kingdom 25264 Primary Examiner-John D. Welsh Attorney, Agent, or FirmLane, Aitken, Dunner & Ziems 51 Dec. 9, 1975 ABSTRACT An electric insulating oil having excellent electrical insulation properties is obtained by incorporating in silicone oil at least one member selected from the group consisting of alkyl fluoranthenes of the generic formula I e w and alkyl pyrenes of the generic formula wherein, R denotes an alkyl group having from one to four carbon atoms and x denotes an integer having a value of from 1 to 4, and when x is an integer of 2 or more, R may be the same or different.

3 Claims, No Drawings ELECTRICAL INSULATION OIL FIELD OF THE INVENTION This invention relates to an electric insulating oil of 5 the type used, in oil-immersed electric apparatus such as. for example, oilimmersed power cables and transformers.

BACKGROUND OF THE INVENTION The necessity for using a nonflammable oil having high thermal resistivity as an electric insulating oil for use in oil-immersed electric apparatus has become widely recognized. To meet this need, silicone oil has come to take the place of mineral oil which has previously served as an electric insulating oil.

Silicone oil is superior to mineral oil in terms of thermal resistivity and nonflammability but is inferior to mineral oil in dielectric breakdown voltage strength as shown in the following table. For this reason, the silicone oil does not, of itself, a fully satisfactory electric insulating oil.

* KF-Jfi-IU, made by The ShinELsu Chemical Industry Co. Ltd. Insulating oil No. 2, prescribed in HS C4320.

In order for silicone oil to be used effectively as an electric insulating oil, therefore, it is desirable that the silicone oil be improved in terms of dielectric breakdown voltage strength.

SUMMARY OF THE INVENTION it is, therefore, an object of the present invention to provide an electric insulating oil having excellent electric insulation by improving the dielectric breakdown voltage strength of the silicone oil without impairing its inherent properties of outstanding thermal resistivity and nonflammability.

Other objects of this invention will become apparent from the following description.

It has now been discovered that when at least one compound selected from the group consisting of specific alkyl fluoranthenes and specific alkyl pyrenes is incorporated into the silicone oil, the resultant mixture possesses high dielectric breakdown voltage strength and therefore serves quite satisfactorily as an electric insulating oil.

The present invention adds to the silicone oil at least one member selected from the group consisting of alkyl fluoranthenes of the generic formula and alkyl pyrenes of the generic formula wherein, R denotes an alkyl group having from one to four carbon atoms and x denotes an integer having a value of from 1 to 4, and when x is an integer of 2 or more, R may be same or different.

DETAILED DESCRIPTION OF THE INVENTION As previously noted, alkyl fluoranthenes which are used in the present invention are those represented by the generic formula:

wherein, R denotes an alkyl group having from one to four carbon atoms and x denotes an integer having a value of from 1 to 4, and when Such is an integer of 2 or more, R may be same or different.

As is clear from the structural formula, these alkyl fluoranthenes have at least one alkyl group selected from the group consisting of methyl, ethyl, propyl and butyl attached at random positions in the fluoranthene nucleus. such alkyl fluoranthenes can easily be obtained by isolation from coal tar and petroleum fractions which are rich in polycyclic aromatic hydrocarbons or by alkylating fluoranthenes with a lower olefin having up to four carbon atoms in the presence of a Friedel-Crafts type catalyst such as aluminum chloride or a solid acid catalyst such as silica-alumina. Generally, an alkyl fluoranthene has mahy isomers. For use in the present invention, a selected alkyl fluoranthene need not be in single isomeric form but may be in the form of a mixture of isomers.

The alkyl pyrenes which are used in the present invention are those represented by the generic fonnula:

in a single isomeric form but may be used in the form of 10 a mixture of isomers.

As previously noted, the present invention incorporates into the silicone oil of at least one compound selected from the group consisting of alkyl fluoranthenes pound will not homogeneously mix with the silicone oil, almost regardless of the particular kind of silicone oil used.

The present invention will be described more specifically by the following description of the preferred embodiments.

EXAMPLE l Various alkyl fluoranthenes and alkyl pyrenes were added, individually and in the form of mixtures, in the percentages shown in Table l to dimethyl polysi- Ioxane (KF-96-l0 made by The Shin-Etsu Chemical Industry Co., Ltd.) and the resultant mixtures were tested for dielectric breakdown strength. The results and alkyl pyrenes of the types described above. The 15 are shown in Table l.

TABLE 1 Dielectric breakdown voltage strength (RV/1.5 mm of oil width) Name of Boiling Amount added by weight) additive point (C) [0.1) (0.2) (0.5) (1.0) (L) (2.5) (5.0) (I00) (ll.0)

Methyl pyrene 390-410 26.3 31.0 37.3 47.0 49.5 48.0 35.3 34.7 30.0 26.8 Ethyl pyrene 400-420 26.3 30.5 37.5 47.3 49.5 43.2 35.6 35.0 30.6 28.6 Butyl pyrene 420-460 26.3 31.0 37.0 46.1 48.3 42.5 37.0 34.9 31.5 27.3 Propyl pyrene 4l0-430 26.3 30.4 36.5 45.2 49.l 48.5 37.4 35.8 32.3 28.0 Dielectric Methyl breakdown fluoranthene 380-440 26.3 30.8 37.0 47.1 49.0 47.5 35.5 34.0 29.7 27.3 voltage Ethyl strength lluoranthene 390-410 26.3 30.3 33.2 46.7 48.5 40.7 38.2 35.5 32.0 28.2 Butyl fluoranthene 410-450 26.3 29.8 37.5 45.5 43.6 42.4 37.0 36.2 3l.0 26.3 Propyl fluoranthene 400-420 26.3 30.2 38.1 46.0 46.3 40.5 36.6 35.1 30.1 26.8 Mixture 1 390-520 26.3 30.6 37.0 46.3 40.5 41.3 35.9 35.8 31.5 26.5 Mixture 2 410-450 26.3 30.0 37.0 45.5 45.8 46.0 37.0 35.5 30.3 27.0 Mixture 3 400-500 26.3 31.0 38.0 46.3 42.6 42.0 36.5 36.4 30.6 27.2 Mixture 4 400-495 26.3 30.3 37.3 45.2 45.2 43.3 37.0 36.0 31.2 28.1

(Note) Mixture l Mixture 2 Pyrene 5 wt% Propyl pyrene 50 wt% Monopropyl pyrene 50 Propyl fluoranthene 50 Dipropyl pyrene 3O Tripropyl pyrene l0 Tetrapropyl pyrene 5 Mixture 3 Mixture 4 Propyl pyrene 50 wt% Propyl fluoranthene 50 wt% Ethyl pyrene 50 Ethyl I'Iuorarlthene 50 the silicone oil amount of such compound added to EXAMPLE 2 should preferably fall in the range of from 0.1 to

by weight based on the silicone oil. If the amount is less than the lower limit 0.1% by weight, the compound fails to provide any appreciable improvement in the dielectric breakdown voltage strength. If, on the other Dimethyl polysiloxane (KF-96-l0 made by The Shin- Etsu Chemical Industry Co., Ltd.) and mixtures obtained by adding van'ous alkyl fluoranthenes and alkyl pyrenes, individually and in the form of mixtures, in a hand, the amount added exceeds the upper limit 10% fixed weight percentage of 0.5% as shown in Table 2 by weight, then the resultant mixture exhibits a degree of dielectric breakdown voltage strength inferior to that obtained by mixtures containing the compound in the range of from 0.1 to 10% by weight and the comwere tested for dielectric properties (dielectric loss tangent and dielectric constant), thermal resistivity (stability against oxidation) and non-flammability (flash point). The results are shown in Table 2.

TABLE 2 Property Dielectric Dielectric Specific volume Stability(*) Flash(**) loss tangent constant resistivity, against poing tan 8 s p (0 cm) oxidation Name of additive 30C 80C 30C 80C 30C 80C (C) None added 0.003 0.003 2.64 2.45 3 X I0 l X l0 0.004 I54 Methyl pyrene 0.004 0.004 2.65 2.46 2 X I0 l X I0 0.004 I53 Ethyl pyrene 0.004 0.005 2.66 2.46 2 X l0 l X [0' 0.004 I54 Butyl pyrene 0.005 0.005 2.68 2.45 2 X IO 1 X I0 0.005 I53 Propyl pyrene 0.005 0.004 2.64 2.47 2 X 10" I X l0" 0.005 I52 Methyl fluoranthene 0.004 0.005 2.65 2.47 2 X IO I X l0' 0.005 I53 Ethyl fluoranthene 0.005 0.005 2.68 2.47 3 X [0 I X l0 0.005 I54 Butyl fluoranthene 0.004 0.005 2.67 2.45 3 X l0 l X l0" 0.004 I55 Propyl fluoranthene 0.004 0.005 2.64 2.48 2 X IO l X 10" 0.004 156 Mixture I 0.003 0.003 2.65 2.47 2 X I0 l X l0" 0.004 I55 Mixture 2 0.005 0.004 2.65 2.47 2 X I0" I X Ill" 0.006 I54 Mixture 3 0.004 0.004 2.64 2.46 2 X I0" I X I0" 0.006 I55 TABLE 2-continued Property Dielectric Dielectric Specific volume Stability(*) Flash loss tangent constant resistivity, against pomg tan 8 e p cm) oxidation Name of additive 30C 80C 30C 80C 30C 80C ("Cl Mixture 4 0.005 0.005 2.64 2.45 3 X I0 I X l0 0.006 154 [Note I) Mixture l Mixture 2 Pyrene wt% Propyl pyrene 50 wt% Monopropyl pyrene SO Propyl fluoranthene 50 Dipropyl pyrene 30 Tripropyl pyrene l0 Tetrapropyl pyrene 5 Mixture 3 Mixture 4 Propyl pyrene 50 wt% Propyl fluoranthene 50 wt% Ethyl pyrenc 50 Ethyl fluoranthene 5O (Note 2) P) Stability against oxidation This value is in terms of dielectric loss tangent which was measured after having heating a given sample at 100C continuously in air for four days.

(**) Flash point measured by the Penalty-Martens method prescribed in HS [(-2265.

It is clear from the preceding two working examples and alkyl pyrenes of the general formula that the additives of the present invention provide the silicone oil with improved dielectric breakdown voltage strength without impairing the outstanding dielectric properties, thermal resistivity and nonflammability inherent to silicone oils. 9

Since the electric insulating oil of the present inven- Rx tion possesses the highly desirable properties described 0 above, it is especially useful for insulation of high-volt age electric apparatus. It may also be combined with a plastic material to form composite insulating material, having utility as insulation for high-voltage oil-filled power cables.

What is claimed is: I. An electric insulating oil comprising a silicone oil and 0.ll0.0% by weight of at least one additive sewherein, R denotes an alkyl group having from 1 to 4 lected from the group consisting of alkyl fluoranthenes carbon atoms and x is an integer of from 1 to 4, and of the general formula when x is an integer of 2 or more, R may be same or different. 2. The electric insulating oil of claim 1, wherein said alkyl fluoranthene is present in the form of a mixture of O isomers.

RX 3. The electric insulating oil of claim 1, wherein said 6 alkyl pyrene is present in the form of a mixture of iso- ITiEI'S. 

1. AN ELECTRIC INSULATING OIL COMPRISING A SILICONE OIL AND 0.1-10.0% BY WEIGHT OF AT LEAST ONE ADDITIVE SELECTED FROM THE GROUP CONSISTING OF ALKYL FLUORANTHENES OF THE GENERAL FORMULA
 2. The electric insulating oil of claim 1, wherein said alkyl fluoranthene is present in the form of a mixture of isomers.
 3. The electric insulating oil of claim 1, wherein said alkyl pyrene is present in the form of a mixture of isomers. 